The present invention relates to the production of hydrocarbons from a subterranean reservoir and more particularly to the enhanced recovery of hydrocarbons by a change in reservoir permeability through controlled reservoir crushing.
It is well known in the oil industry that enhanced recovery techniques are employed to produce additional volumes of hydrocarbons from subterranean reservoirs after production by primary recovery techniques have declined to an uneconomical level. Primary recovery techniques include natural flow, gas lifting and pumping methods. There are hydrocarbon-bearing reservoirs, which even though containing large quantities of hydrocarbon, are incapable of being produced by primary recovery techniques. Recognition of the large amount of residual hydrocarbon in many reservoirs has led to the use of the so-called enhanced, or secondary, recovery techniques which have as their purpose the economical recovery of additional quantities of the residual hydrocarbon known to be present in the reservoir. In those enhanced recovery techniques, means is introduced into the reservoir to displace hydrocarbons therein to a suitable production system through which the hydrocarbons may be withdrawn to the surface of the earth. One commonly known secondary recovery technique involves injecting fluid, such as a gas, into a partially depleted reservoir through an injection system to drive hydrocarbons toward a production system from which the hydrocarbons are produced along with portions of the driving fluid. When the ratio of driving fluid to hydrocarbons reaches an uneconomical level, the reservoir is normally abandoned, even though a substantial amount of residual hydrocarbons still remains in the reservoir.
In general, large quantities of fluid are employed in such processes because pressures in the thousands of psig are normally employed. Often incremental hydrocarbon recovery due to the enhanced recovery is not as great as is desired because of the existence of rather wide variations in the permeability of various portions of such formations. The injected driving fluid tends to follow selective paths through the relatively more permeable channels of the formation from the injection well to the production well. Because of this channeling tendency, the driving fluid fails to contact the portions of the hydrocarbons that reside in the relatively less permeable portions of the formation. The sweep efficiency of the operation, as a result, is relatively poor. Because of this poor sweep efficiency, a large portion of the recoverable hydrocarbons in the reservoir is bypassed, seriously limiting the overall effectiveness and efficiency of the recovery operation.
Even when the reservoir exhibits a relatively uniform permeability throughout, a situation referred to as instability channeling may develop in those instances where the viscosity of the injected displacing fluid is signficantly less than the viscosity of the in-situ reservoir hydrocarbons. In this situation, the less viscous displacing fluid tends to develop channels or fingers which may be caused by points of minute heterogeneities in the reservoir. These channels of displacing fluid tend to become extended in the direction of flow and travel at a faster rate than the remainder of the injected fluid, thus again resulting in poor sweep efficiency.
It is, therefore, an object of the present invention to enhance the sweep efficiency of an injected fluid during hydrocarbon recovery from a subterranean reservoir by altering the permeability of the reservoir through a controlled in-situ reservoir crushing technique.